Suikawari (watermelon splitting) is a somewhat popular summertime game held at beaches, festivals, and picnics.
The most common way it is played is: A watermelon is laid out, sometimes on a tarp, and participants attempt to smash it open. Each is blindfolded, spun around three times, and handed a bokken to strike with. The first to crack the watermelon open wins. After it is broken the chunks of watermelon are shared among participants.
This shows up fairly often in manga and anime, for example, in the Ranma manga there is a beachside battle version of this and in Azumanga Doiah Tomo wants to break the watermelon with her hand via a karate chop.